A blotchy sunburn happens because your skin doesn’t receive UV exposure evenly. Some areas get more protection than others, whether from how you applied sunscreen, where your clothes sat, how much you sweated, or simply because different parts of your skin respond differently to the same amount of sun. The result is a patchwork of deep red, light pink, and untouched skin instead of one uniform color.
Uneven Sunscreen Is the Most Common Cause
The most likely reason your sunburn looks blotchy is inconsistent sunscreen coverage. Most people miss spots or apply too thinly in certain areas without realizing it. But even a perfect application can break down unevenly over the course of a few hours.
Sweat is a major factor. Research published in Skin Research and Technology found that perspiration reduces SPF through two separate mechanisms: it physically washes sunscreen off the skin, and it redistributes the protective film into an uneven layer. As sweat droplets form underneath the sunscreen, they push the product around, creating gaps in coverage. Where two droplets expand toward each other, UV-filtering ingredients briefly concentrate along the border between them, leaving the surrounding skin exposed. The net effect is a checkerboard of well-protected and barely-protected zones across your skin.
Friction makes this worse. Toweling off, adjusting clothing, leaning against a chair, or rubbing your face all strip sunscreen from contact points while leaving it intact elsewhere. Water exposure from swimming or splashing has the same effect. Every time you disturb the sunscreen film, you create another patch of vulnerable skin.
Your Skin Itself Burns Unevenly
Even with zero sunscreen in the picture, a perfectly even sunburn is rare. Different areas of your body have different skin thickness, different amounts of natural pigment, and different blood supply. Your forearms, for example, are typically more sun-adapted than your shoulders or lower back, which rarely see direct light. Thinner skin over your collarbones or the tops of your feet burns faster than the thicker skin on your upper arms.
Freckles and moles also play a role. Skin with more concentrated melanin absorbs UV differently than surrounding tissue, so you can end up with a mottled look even from uniform exposure. If you have naturally uneven skin tone, a sunburn will amplify those differences rather than mask them.
Certain Plants Cause Irregular Burn Patterns
If your blotchy burn has oddly specific shapes, like streaks, drip marks, or handprint-like outlines, you may be dealing with a condition called phytophotodermatitis. This happens when a natural plant chemical called furanocoumarin gets on your skin and then reacts with sunlight, causing localized burns or dark discoloration that can look dramatically different from the surrounding skin.
The most common culprits are limes and other citrus fruits, celery, parsley, parsnips, carrots, dill, fennel, figs (especially the sap), and hogweed. Squeezing limes into drinks at a barbecue, handling celery while cooking outdoors, or brushing against wild parsnips on a hike can all leave invisible traces of furanocoumarin on your skin. Hours later, those exact spots burn or darken while the rest of your skin looks fine. The resulting patches often follow the pattern of how the juice dripped or where your fingers touched.
Medications That Increase UV Sensitivity
Certain medications make your skin more reactive to sunlight, and the effect isn’t always uniform. Common photosensitizing drugs include doxycycline and other tetracycline antibiotics, ibuprofen, naproxen, some blood pressure medications, and isotretinoin (used for acne). St. John’s Wort, an herbal supplement for mood, is another well-known trigger. Even some topical products, including retinoids like tretinoin, can make the areas where they’re applied burn much faster than untreated skin.
If you’re on one of these medications, the blotchiness often shows up as areas that burned far more severely than you’d expect for your time in the sun. The parts of your body with the thinnest skin or the most direct exposure tend to react the strongest, creating a patchy appearance.
Blotchiness During Healing Is Normal
If your sunburn looked relatively even at first but has become blotchy over the following days, that’s the normal healing process. When UV damages your skin, blood vessels dilate and immune cells rush to repair the injury. Some skin cells recover while others die and eventually peel off. This doesn’t happen on a neat, synchronized schedule across your entire body.
Peeling typically starts a few days after the burn and continues for about a week, though severe burns can take several weeks. During this time, patches of dead skin sit alongside fresh, newly exposed skin underneath, creating a mottled look. The temptation to peel off loose skin makes this worse, because you end up removing skin in some areas before it’s ready while leaving other spots intact. Your skin will look uneven until the peeling process finishes and the new skin underneath has had time to normalize.
Dark or Light Spots That Linger
After a sunburn fully heals, you may notice that some areas remain darker or lighter than the surrounding skin. This is called post-inflammatory pigmentation, and it’s your skin’s response to the injury it just went through. Darker spots form when inflammation triggers excess melanin production in certain areas. Lighter spots can appear where the burn was severe enough to damage pigment-producing cells.
These color differences are more noticeable and longer-lasting in people with darker skin tones, where the contrast between affected and unaffected skin is more pronounced. Dark spots from a mild to moderate burn typically fade on their own over weeks to months. Light spots from a severe burn, however, can sometimes be permanent, because the cells responsible for pigment were destroyed rather than just irritated.
Keeping the affected skin moisturized and protected from further sun exposure gives it the best chance of returning to its normal shade. Additional UV exposure on healing skin can deepen the discoloration and extend the time it takes to even out.